The present invention relates to the field of chip removing machining and particularly to a milling insert and a milling cutter tool in which the milling insert is mounted. The milling insert is shaped as a trigon shape having a number of cutting edges and is adapted to be mounted in a milling cutter body of the milling cutter tool.
Previously known trigon-shaped milling inserts are shaped to be mounted substantially radially in a milling cutter body, the axis of a centrally placed mounting hole being directed tangentially in relation to the milling cutter body. Such a mounting requires a considerable recess in the milling cutter body so that mounting of a milling insert could be accomplished, which in turn means that the milling cutter body at a certain radius only can receive a certain a number of milling inserts. Furthermore, radial mounting means that the strength of the milling insert to a certain extent depends on the extension thereof in the axial direction of the mounting hole.
Tangentially mounted milling inserts can be seen in, for instance, WO 2005/075135, U.S. Pat. No. 6,872,034 and U.S. Pat. No. 7,014,396.
It is desirable to provide an improved trigon-shaped milling insert, which can be mounted tangentially in the milling cutter body of a tool and which furthermore is provided with dedicated support surfaces for an improved abutment against a pocket of the milling cutter body.
It is also desirable that the support surfaces are placed on the milling insert as well as in the milling cutter body in such a way that the cutting forces in a milling operation contributes to an increased abutment against the pocket as well as to minimizing the torque to turn the milling insert radially out of the pocket.
It is also desirable to provide a milling cutter tool for such a milling insert.
An aspect of the invention relates to an indexable milling insert having a trigon shape, which milling insert comprises a mounting hole placed centrally in the milling insert, an upper side and a lower side, which sides are parallel with each other and act as an alternating first and second support surface. The milling insert is provided with major cutting edges, which are oriented perpendicularly to the axis of the mounting hole as well as arranged in such a way that a turning of the milling insert around the center of the mounting hole alternatively a flipping of the milling insert into an alternative cutting position provides an identical position of the major cutting edges in relation to a workpiece. In this connection, the major cutting edges of the milling insert are placed in the milling insert, when the same is tangentially mounted in a cutting body, in such a way that, in the shown top view, the shortest distance of the major cutting edges to the axis of the hole is smaller than the distance of a third support surface to the axis of the hole.
Furthermore, milling inserts may be shaped so that the distance in top view between each major cutting edge and an adjacent third support surface grows in the direction from an associated nose edge.
Furthermore, the milling insert may comprise three major cutting edges placed on the edge of the respective lower/upper side near a cutting corner.
The milling insert may be provided with third support surfaces placed along the sides of the milling insert at a right angle in relation to the imaginary extension of the first support surface.
The milling insert may be provided with additional third support surfaces placed along the sides of the milling insert at a right angle in relation to the imaginary extension of the second support surface.
The third support surfaces may be pair-wise arranged in direct connection with and on both sides of a cutting corner of the milling insert.
The milling insert may be provided with clearance surfaces placed in direct connection with the first support surface and the second support surface in the extension of the respective major cutting edges along the edge of the respective first and second support surface so that the clearance surfaces form an acute edge angle with the imaginary extension of the support surfaces.
The milling insert may be provided with corner surfaces placed at an angle to and in direct connection with the third support surfaces and at a right edge angle in relation to the imaginary extension of the first and the second support surface.
The milling insert may furthermore be shaped so that each corner surface and adjacent third support surface connect to each other under an angle β, where 10°<β<20°, preferably is 13°<β<17°. Furthermore, a milling insert may be shaped so that each major cutting edge forms an angle φ with the appurtenant third support surface, which angle φ is of the same size as the angle β±2°.
All support surfaces of the milling insert may be completely planar.
The major cutting edge of the milling insert may also transform directly into a nose edge.
The milling insert may furthermore comprise six minor cutting edges, each one having an extension from the first support surface toward the second support surface at a substantially parallel orientation with the symmetry axis of the mounting hole.
The milling insert may also be shaped so that each minor cutting edge is of the same size as the third support surface in a direction parallel with the axis of the hole. Each minor cutting edge may also connect directly to a nose edge.
Furthermore, all cutting edges connected to each other may be situated in the same plane.
An aspect of the invention also relates to a milling cutter tool comprising a milling cutter body having a plurality of insert pockets. Each insert pocket is intended to receive a milling insert shaped according to anyone of the above-mentioned milling inserts.
The insert pockets of the milling cutter tool may comprise a main support surface against which the milling insert is arranged to abut by the first/second support surface thereof.
The insert pocket of the milling cutter tool may also comprise a wedge-shaped support pocket having primary support surfaces arranged, in which support pocket the milling insert is mounted with abutment of the pair-wise arranged third support surfaces thereof against the primary support surfaces in order to, by means of arising cutting forces in a milling operation, provide an increased abutment force of the milling insert against the support pocket.
The support pocket of the milling cutter tool may furthermore be provided with a secondary support surface against which another one of the third support surfaces of the milling insert is arranged to abut.